In close quarter combat, typically in the ranges of 2-800 meters, soldiers are required to rapidly acquire, identify, and accurately fire on enemy targets. Soldiers may use weapon-mounted sights with visible and infrared light sources to assist in the aiming process during daytime and nighttime missions. These sights may be mounted on handheld weapons such as the M4A1 carbine and other small arms and are used to provide better target observation, illumination, and marking.
Traditional weapon-mounted sights utilize red dot sights that incorporate a light emitting diode (LED) as a source of illumination in conjunction with a pinhole aperture. Light emitted from the LED and passing through the pinhole is reflected by an optical element and forms an aim point that can be seen by a shooter looking through the close quarter combat sight. Because the LED has a relatively large emitting area and practical transmission and machining capability limitations limit how small a pinhole can be used, the resulting aim point is relatively large in size. Such a large aim point is undesirable and impairs accuracy especially when aiming at a relatively small target or a target at a relatively long distance.
Red dot sights may be used both during the day without assistance or at night with the assistance of a night vision device such as a monocular or goggle. Red dot sights utilizing tritium (a radioactive isotope) exist, but suffer because the brightness can not be increased during the day and decreased during the night to be compatible with night vision devices.
A dichroic coating is commonly used on a lens surface of a red dot sight to partially reflect or transmit light and to provide a simultaneous view of the red dot and the target scene. Because a visible LED has a relatively weak, apertured light intensity, the optical element typically needs to have a highly reflective coating if a significant amount of the light energy is to be reflected toward the shooter. This highly reflective coating effectively blocks light from the target scene in transmission at wavelengths similar to those being reflected from the LED. Therefore if the a red dot sight employs a red LED, the optical element commonly has a coating that reflects a relatively high percentage of the red light energy from the LED to increase the brightness of the LED visible to the eye, and thus also blocks a high percentage of red light from the target scene. The result is the target scene has an undesirable blue tint. Not only does this blue tint cause the scene to look unnatural, it also impairs one's ability to use the sight with two eyes open because one eye sees the target scene in normal color while the eye seeing the target scene through the sight sees a bluish scene. The blue tint also makes target acquisition difficult in low light conditions such as dusk or dawn because a lack of light transmission. Depending on the nature of the reflective coating, the coating impairs the transmission of light in a portion of the electromagnetic spectrum that the night vision device is sensitive thereby reducing the performance capabilities of the night vision device, in turn affecting the ability of the operator to detect and direct fire on the target. This can be quite distracting. The large aim point and the distorted color of the target scene are two major limitations of existing red dot sights.
Traditional red dot sights have optical elements having spherical optical elements or in some cases holographic elements. With such elements, parallax is present to a significant degree. That is, as the observer looking through the red dot sight moves his eye relative to the sight optical aperture, the point of aim moves with respect to the target. This results in a loss of aiming accuracy. Also, since different shooters hold their eye differently relative to the sight, no single boresight or zero setting of the sight is suitable for all users. This means that each shooter may need to boresight or zero the red dot sight for himself.